Dynamic Response Analysis Of Long Span Transmission Tower-line System Under Extreme Environmental Conditions

Long span transmission tower-line system is a vital lifeline to power system. Exposing in environment, the system must be robust enough to bear destructive force in extreme environmental conditions. The tower may collapse under extreme environmental loading such as tornado, earthquake, snow and ice disaster. The iced transmission line galloping may occured also. These accidents influence the safety of power system seriously. In this paper, dynamic response of long span transmission tower-line system under extreme environmental conditions is analyzed by finite element method. The analysis results are provided for electricity sector and they are helpful for on-line monitoring of tower-line system.Firstly, a finite element model of long span transmission tower-line system is built. Modal analysis is done on different models, such as span tower, anchor tower, and tower-line system. Natural modes and frequencies are extracted. The results show that natural frequency value of span tower reduces when elevator well hole is considered. However, the value reduces much more when transmission line and anchor towers are all considered.Secondly, static and dynamic response analysis of long span transmission tower under tornado loading is calculated. Material nonlinearity is considered and three different cases of wind loading(tower surface and wind velocity are at 0°,45°,90°angle) are discussed. Deformation and stress are obtained. The results show that tower is safe under F2 grade tornado in static analysis. On the other hand, plastic deformation causes tower damaged in dynamic analysis with a maximum wind velocity 100m/s. However, the deformation and stress are more significant in 45°angle case either in static or dynamic analysis.Thirdly, time-history analysis of tower under earthquake loading is studied to obtain deformation and stress of structure. The results show that deformation in horizontal direction is major and the value gets larger as height increases. Maximum stress of tower is lower than ultimate stress which reveals that the tower has a good resistance in VII magnitude intensity earthquake.Finally, galloping of iced line is studied. Galloping mechanisms and conditions of both Den Hartog model and O.Nigol model are explained. A model of iced line is built by finite element method. A program is compiled to analyze transmission line galloping. The simulation results show that vertical vibration takes a leading role in galloping, the trace of middle node can be portrayed as an ellipse.